4.1.4.1. Configure Azure Load Balancer

4.1.4.1. Configure Azure Load Balancer

💡 First Principle: Azure Load Balancer ensures high availability and scalability for applications by distributing network traffic at Layer 4 (TCP/UDP) across multiple healthy backend resources, preventing any single resource from becoming a bottleneck.

Scenario: You have a backend processing service running on multiple Virtual Machines within an Azure Virtual Network. This service is accessed by other internal applications and does not need direct internet exposure. You need to distribute incoming requests evenly across these VMs and ensure only healthy VMs receive traffic.

What It Is: Azure Load Balancer operates at Layer 4 (TCP/UDP) of the OSI model, distributing traffic to backend resources.

Types of Azure Load Balancer:

• Public Load Balancer:
  • Purpose: Distributes internet-facing traffic to Azure VMs.
  • Frontend: Requires a public IP address.
• Internal Load Balancer:
  • Purpose: Handles traffic within a virtual network.
  • Frontend: Uses a private IP address.

Shared Components Both types use backend pools (target resources), health probes (monitoring), and load balancing rules (traffic logic).

Configuring a Standard Load Balancer:

1. Create the Load Balancer (Standard SKU).
2. Define the frontend IP configuration.
3. Add backend pool members.
4. Set up health probes.
5. Create load balancing rules.

Visual: Azure Load Balancer Flow

⚠️ Common Pitfall: Treating the Basic SKU Load Balancer as a live choice. Basic Load Balancer was retired on 30 September 2025, and creation of new Basic load balancers closed on 31 March 2025. Existing Basic load balancers keep running, but they are unsupported and carry no SLA. Standard is the only SKU available for new deployments, and it is what adds Availability Zone redundancy, higher scale, and secure-by-default behaviour. Expect the exam to test migration to Standard rather than a Basic-versus-Standard choice.

Key Trade-Offs:

• Public vs. Internal: Public load balancers provide internet accessibility but increase the attack surface. Internal load balancers enhance security by keeping traffic private but cannot be accessed from the internet.

Reflection Question: How does configuring an Internal Azure Load Balancer with backend pools and health probes fundamentally ensure high availability and scalability for internal services by preventing any single VM from becoming a bottleneck?